This invention relates to catalytic reactor operating techniques wherein a liquid phase reactor is co-treated with a gaseous phase reactant. In particular, it relates to an improvement for contacting multi-phase reactants in a fixed porous catalyst bed under continuous operating conditions, including methods and apparatus for controlling fluid flow in the reactor.
Chemical reactions between liquid and gaseous reactants present difficulties in obtaining intimate contact between phases. Such reactions are further complicated when the desired reaction is catalytic and requires contact of both fluid phases with a solid catalyst. In the operation of conventional concurrent multiphase reactors, the gas and liquid under certain circumstances tend to travel different flow paths. The gas phase can flow in the direction of least pressure resistance; whereas the liquid phase flows by gravity in a trickle path over and around the catalyst particles. Parallel channel flow and gas frictional drag can make the liquid flow non-uniformly, thus leaving portions of the catalyst bed underutilized due to lack of adequate wetting.
Various attempts have been made to avoid maldistribution, such as the provision of multiple layers of catalyst with interlayered redistributors located along the reactor longitudinal axis. Numerous multi-phase reactor systems have been developed wherein a fixed porous bed of solid catalyst is retained in a reactor. Typically, fixed bed reactors have been arranged with the diverse phases being passed concurrently over the catalyst, for instance as shown in U.S. Pat. Nos. 4,126,539 (Derr et al), 4,235,847 (Scott), 4,283,271 (Garwood et al), and 4,396,538 (Chen et al). While prior reactor systems are satisfactory for certain needs, efficient multi-phase contact has been difficult to achieve for many fixed bed applications.
In the petroleum refining industry, multi-phase catalytic reactor systems have been employed for dewaxing, hydrogenation, desulfurizing, hydrocracking, isomerization and other treatments of liquid feedstocks, especially heavy distillates, lubricants, heavy oil fractions, residuum, etc,. In a preferred hydrodewaxing process the catalyst comprises a medium pore siliceous zeolite having a constraint index of about 1 to 12, for example, an acidic ZSM-5 type pentasil aluminosilicate having a silica to alumina mole ratio greater than 12. It is an object of the present invention to provide a unique reactor system, including concurrent operating techniques and apparatus, for improved treatment of liquid with a gaseous reactant in a reactor containing a porous fixed bed of solid catalyst. It is a further object to provide a technique for operating multi-phase reactors under controlled flow conditions to maintain substantially uniform gas-liquid contact, while minimizing flow and temperature maldistribution patterns and providing downwardly gravitating liquid under substantially uniform liquid flux to assure relatively uniform wetting of the catalyst particles.